(i) Field of the Invention
The present invention relates to a trunk visceral fat measuring method and apparatus, a trunk skeletal muscle amount measuring apparatus, a trunk subcutaneous fat measuring method and apparatus, and a trunk visceral and subcutaneous fat measuring method and apparatus.
(ii) Description of the Related Art
A technique for estimating body fat tissues by use of a bioelectrical impedance method has been spread as a technique for measuring body fat tissues and a body fat percentage. In reality, however, it does not measure fat tissues directly but electrically measures fat free tissues other than the fat tissues in which water is dominant. In particular, in whole body measurement, a conventional type (between-one-hand-and-one-foot lead system) models a body part between one hand and one foot in a supine position by one cylinder. As simple techniques, a between-palms lead system which makes a measurement in a standing position, a between-soles lead system integrated with a scale, and a technique for measuring an impedance by dividing a body into the upper limb and the lower limb, the upper limb, the lower limb and the trunk or five segments, e.g. the left and right upper extremities, the left and right lower extremities and the trunk, and applying a cylindrical model to each segment have been increasing popular. Further, a simplified impedance measurement technique comprising disposing current applying electrodes and voltage measuring electrodes around the navel of the trunk and measuring the impedance of the abdomen to estimate a visceral fat tissue amount has been applied for patent (refer to Patent Literatures 1 and 2).
Patent Literature 1
    Japanese Patent Application No. 3,396,677Patent Literature 2    Japanese Patent Application No. 3,396,674
However, the usefulness of information of body fat for screening lifestyle-related diseases such as diabetes, hypertension and hyperlipemia has been receiving particular attention, and the significance of measurement of visceral fat adhered or accumulated around the splanchnic organs has been increasing day by day.
Visceral fat tissues are fat tissues distributed around the abdomen of the trunk in a concentrated manner and have been determined by an image of a cross-sectional area of the fat tissues of the abdomen by X-ray CT or MRI. However, this requires a large-scale apparatus and has problems of X-ray exposure and high costs and is therefore not suited for measurement in the field and household. Consequently, the visceral fat tissues are generally estimated from correlation with the fat tissues of the whole body or correlation with the fat free tissues of the whole body and cannot secure adequate reliability for screening.
Recently, a method comprising disposing electrodes around the navel of the trunk and measuring the internal impedance of the trunk to estimate visceral fat tissue information has also been under development. However, this method is based on significant correlation existing among a skeletal muscle tissue layer, a subcutaneous fat tissue layer and visceral fat tissues and based on the premise that if information of any of these tissues can be acquired, the information can be roughly estimated. Therefore, while good results can be expected for highly independent, healthy subjects who can have highly significant correlation among the tissues, significant errors may be contained in measurement results for subjects having different correlations among the tissues, e.g. subjects having significantly enlarged visceral fat tissues and having significantly low correlation between the subcutaneous fat tissue layer or skeletal muscle tissue layer and the visceral fat tissues. That is, even this method under development has a significant problem in measurement on paralyzed patients and patients who need nursing care, particularly patients confined to bed, although the method can somehow make the measurement on healthy subjects capable of leading independent life regardless of where on the whole circumference of the navel the electrodes are disposed.
Further, this method under development is said to be a sophisticated technique in that it passes a current through a tissue part to be measured from the surface of the abdomen to acquire an impedance value associated with the internal tissue. However, it is an actual situation that measured impedance information itself has hardly useful sensitivity to visceral fat tissues due to the problem of the internal structure of the trunk which is a body part to be measured. That is, the trunk which is a body part to be measured is thick and short and has a multiple structure, i.e. a structure in which the visceral fat tissues to be measured together with splanchnic organ tissues and spinal tissues are covered with a skeletal muscle tissue layer showing very good electrical conductivity and the skeletal muscle tissue layer is covered with a subcutaneous fat tissue layer showing very poor electrical conductivity. In particular, around the visceral fat tissues to be measured, splanchnic organ tissues showing lower electrical conductivity than the skeletal muscle tissue layer and visceral fat tissues of poor electrical conductivity which are adhered and accumulated to the splanchnic organ tissues are dominant and constitute a complicated structure, resulting in very poor electrical conductivity of the tissues under the skeletal muscle tissue layer is very poor. For this reason, even if current applying electrodes are simply disposed around the abdomen, most of current passes through the skeletal muscle tissue layer, and current density distribution is observed from surface measuring electrodes as electrical potential distribution dominated by the skeletal muscle tissue layer. Further, applied current density distribution is determined from the surface area of the current applying electrode or the width of the electrode in the abdominal circumferential direction, and observation of information in a spreading resistance region showing high current density in the subcutaneous fat tissue layer right underneath the electrodes.
Further, since the trunk which is a body part to be measured is thick and short, sensitivity in the subcutaneous fat tissue layer in the current density concentrating (spreading resistance) region right underneath the current applying electrodes becomes high. Further, since the skeletal muscle tissues have very high electrical conductivity as compared with the fat tissues, most of current having passed through the subcutaneous fat tissue layer returns to the opposing current applying electrode via the skeletal muscle tissue layer and the subcutaneous fat tissue layer, and as a result, electrical potential distribution in the tissues under the skeletal muscle tissue layer is significantly distorted by the skeletal muscle tissue layer. Thus, in the conventional method, most of electrical potential measured is information of the subcutaneous fat tissue layer, energization of the visceral fat tissues to be measured, i.e. the splanchnic organ tissues and the visceral fat tissues adhered and accumulated therearound can be hardly expected, and only information with a very low measurement sensitivity of not higher than 10% of all impedance measurement section can be acquired.
To avoid these problems, a method comprising incorporating abdominal circumferential length having high correlation with a subcutaneous fat tissue layer area into an estimation expression to prevent an increase in estimation error is conceived. However, this method is merely indirect estimation by correlation between constituent tissues and is hardly called a measurement method having energization sensitivity required in the middle of the abdomen. That is, individual errors deviated from statistical correlation design cannot be assured, and particularly when the amount of the subcutaneous or visceral fat tissues is abnormally large or the intermediate skeletal muscle tissue layer is large or small, a significant error may occur. The subcutaneous fat tissue layer area has high correlation with the abdominal circumferential length, because the trunk of human being is concentric tissue arrangement design, the subcutaneous fat tissue layer is the outermost layer and its area is determined by outer circumferential length and subcutaneous fat tissue thickness.
To dispose electrodes on the trunk, a four-electrode technique is generally used. This method passes a current through the body of a subject and measures a potential difference which has occurred in a body part to be measured of the subject by the applied current so as to measure a bioelectrical impedance in the measured body part. When the four-electrode technique is applied to a thick and short body part to be measured such as the trunk, a current density concentrating region (or a spreading resistance region) when a current has just started to spread is, for example, right underneath current applying electrodes, so that a large potential difference occurs in the vicinity of the subcutaneous fat tissue layer and constitutes most of potential difference measured between voltage measuring electrodes. To reduce the influence by the spreading resistance, it is important to dispose the current applying electrodes and the voltage measuring electrodes with sufficient distance secured therebetween. Since general measurement is carried out under conditions which can secure a long measurement section and sufficient distance between the voltage measuring electrodes, so-called S/N sensitivity (N is the influence (noise) by the spreading resistance, and S is a signal measured between the voltage electrodes) should be secured sufficiently. However, in the case of a thick and short body part to be measured such as the trunk, when the voltage measuring electrodes are moved away to secure distance from the current applying electrodes so as to render N small, the distance between the voltage measuring electrodes becomes small. As a result, S becomes small, resulting in deterioration in S/N. Further, the spreading resistance portion showing high current density is a subcutaneous fat tissue layer portion and subjects liable to become obese with thick fat are common, so that N becomes quite large and S/N further deteriorates. Thus, when the four-electrode technique is applied to a thick and short body part to be measured such as the trunk, it is expected to be quite impossible to secure useful S/N sensitivity to visceral fat tissues merely by disposing the electrodes around the navel. S/N will be further described in detail in descriptions about Examples to be described later.
An object of the present invention is to solve the above problems of the prior art and provide a method and apparatus which can secure sensitivity required for measurement even in splanchnic organ tissue and visceral fat tissue regions having low electrical conductivity and measure information of fat tissues accumulated in the trunk, particularly, fat tissues adhered and accumulated around splanchnic organ tissues and fat tissues accumulated in the subcutaneous layer with high accuracy and with ease.
Another object of the present invention is to provide a method and apparatus which can secure sensitivity required for measurement even in splanchnic organ tissue and visceral fat tissue regions having low electrical conductivity and measure information of fat tissues accumulated in the trunk, particularly, fat tissues adhered and accumulated around splanchnic organ tissues with high accuracy and with ease and a health guideline advising apparatus.
Another object of the present invention is to provide a method and apparatus which can secure sensitivity required for measurement even in splanchnic organ tissue and visceral fat tissue regions having low electrical conductivity and measure information of fat tissues accumulated in the trunk, particularly, fat tissues adhered and accumulated around splanchnic organ tissues and fat tissues accumulated in the subcutaneous layer and subcutaneous fat tissue layer information simultaneously only by switching.
Another object of the present invention is to provide a trunk visceral fat measuring method and apparatus which can secure sensitivity required for measurement even in splanchnic organ tissue and visceral fat tissue regions having low electrical conductivity, measure information of fat tissues accumulated in the trunk, particularly, visceral fat tissues adhered and accumulated around splanchnic organ tissues and subcutaneous fat tissues accumulated in the subcutaneous layer with high accuracy and ease, and provide measurement result information having high measurement reproducibility and high reliability and excluding error factors ascribable to intricately mixed tissues.